Green poop is almost always harmless. The most common causes are eating green vegetables, taking iron supplements, or having food move through your digestive system faster than usual. In most cases, your stool color will return to its normal brown within a day or two once the trigger passes.
How Stool Gets Its Color
Your liver produces bile, a bright green fluid that helps digest fats. As bile travels through your intestines, bacteria break it down and gradually change its color from green to yellow to brown. That final brown shade is what most people see on a regular basis.
When something speeds up digestion, food passes through the large intestine too quickly for bacteria to finish converting the bile. The result is stool that still carries that original green tint. This is why diarrhea from any cause often comes out green: it’s not a separate problem, just a sign that transit time was shorter than usual.
Foods That Turn Stool Green
The chlorophyll that makes vegetables green can do the same to your stool. Spinach, kale, and broccoli are the most common culprits, but avocados, fresh herbs, matcha, and even pistachios contain enough chlorophyll to shift the color noticeably. You don’t need to eat an unusual amount. A large salad or a green smoothie can be enough.
Blueberries and other dark purple fruits can also produce green stool, since the blue and purple pigments mix with yellow bile to create a greenish shade. Artificial food dyes are another frequent trigger. Brightly frosted cupcakes, flavored drink mixes, ice pops, and candy continue tinting whatever they touch as they pass through your digestive system. If your stool turned green a day after a birthday party or a treat with vivid coloring, that’s likely the explanation.
Medications and Supplements
Iron supplements are one of the most reliable causes of green (or dark greenish-black) stool. The iron itself changes color as it’s processed, and this is a completely expected side effect rather than a sign of a problem.
Several other common medications can also shift stool color toward green. Antibiotics disrupt the balance of gut bacteria responsible for converting bile, which can leave stool greenish until your bacterial population recovers. Bismuth subsalicylate, the active ingredient in some antidiarrheal medications, reacts with sulfur in your digestive tract and can turn stool dark green or black. Antacids containing aluminum hydroxide sometimes produce a greenish tint as well.
Infections and Rapid Transit
Stomach bugs are a common cause of suddenly green, loose stool. Bacteria like Salmonella, the parasite Giardia, and viruses like norovirus all cause your gut to flush its contents faster than normal. When everything moves through at that speed, bile stays green. The color itself isn’t the concern in these cases. What matters more is the accompanying symptoms: watery diarrhea, cramping, nausea, fever, or signs of dehydration like dark urine and dizziness.
If green stool shows up alongside those symptoms and lasts more than two or three days, an infection is worth investigating. Most resolve on their own, but prolonged diarrhea with fever or blood in the stool warrants a call to your doctor.
Green Stool in Babies
Green poop in infants has its own set of causes and is common enough that pediatricians field questions about it constantly. Newborns pass meconium, a dark greenish-black stool, in the first few days of life. This is completely normal.
In breastfed babies, green stool sometimes happens when a baby doesn’t finish feeding on one side before switching. The earlier milk (foremilk) is lower in fat, and skipping the fattier hindmilk can affect digestion and produce greenish stool. Babies on protein hydrolysate formula, which is designed for infants with milk or soy allergies, also tend to have greener stool as a normal side effect of that formula type. Breastfed infants who haven’t yet developed a full population of intestinal bacteria may also pass green stool in the early weeks. As with adults, diarrhea in babies speeds transit and keeps bile green.
How Long It Typically Lasts
Diet-related green stool usually clears up within one to three days once you stop eating the food responsible. If iron supplements are the cause, green or dark stool will persist for as long as you’re taking them, and that’s fine. After a stomach bug, stool color normalizes as your digestion returns to its usual pace, typically within a few days of symptoms resolving.
Green stool that persists for weeks without an obvious dietary or medication explanation is worth mentioning at your next appointment. Ongoing changes in stool color, especially paired with unexplained weight loss, persistent cramping, or visible blood, can point to conditions that affect how well your intestines absorb nutrients. On its own, though, a green bowel movement is one of the least concerning color changes your stool can make.